4946
Ind. Eng. Chem. Res. 1999, 38, 4946-4950
Separation of Cr(VI) on Chitosan Membranes Zofia Modrzejewska* and Wladyslaw Kaminski Faculty of Process and Environmental Engineering, Technical University of -Lo´ dz´ , ul. Wo´ lczan˜ ska 213, 90-924 L -o´ dz´ , Poland
Chitosan membranes were used for hexavalent chromium removal. Investigations covered membranes produced by phase inversion (wet-method). The modifications of membranes were made by acetylated and cross-linked Cu(II). In the experiments chitosan produced by the Sea Fisheries Institute, Poland, was used. The metal ions were removed on chitosan membranes during membrane processes. The modifications and the effect of the pH of the solution on the separation properties of membranes were determined. The concentration of metal ions was measured by the method of inductively coupled plasma (ICP) atomic emission spectrometry. Introduction Chromium compounds at the VI degree of oxidation are of great practical importance. CrO3 is a very potent oxidizing agent. It is applied first of all in chrome plating and, when dissolved in acetic acid, as an oxidizing agent in organic chemistry. However, this is a strongly toxic compound; hence, research has been carried out on its removal from wastewater produced by industrial electroplating plants.1 Separation is carried out by classical methods or membrane techniques.2-6 The separation of metal ions by the classical methods is accomplished by precipitation, evaporation, ion exchange, or adsorption.2,3 Removal of metal ions by the membrane techniques is carried out mainly by high-pressure techniques (reverse osmosis and nanofiltration). Electrodialysis, Donnan dialysis, or liquid membranes are also applied.4 Separation of Cr(VI) ions was carried out most frequently by the classical methods, which included the reduction of hexavalent chromium to Cr(III) in acid medium and then, as a result of addition of NaOH to Cr(III) solutions, precipitation of hydrated oxide:
Cr
3+
-
+ OH f Cr2O3(H2O)n
Cr(VI) ion separation by means of combined classical and membrane techniques was described by Fabiani.5,6 First, chromium(VI) was reduced to chromium(III) by Na2S2O5 or FeCl2; then, chromium ions were precipitated with sodium hydroxide and subjected to ultrafiltration. Over a 100-fold increase of chromium concentration in the retentate relative to the initial (charge) solution was achieved, and permeate containing
